This invention relates to apparatus for monitoring rotating machinery and in particular to a system for monitoring vibration and current signals in a turbine-generator.
In large machines such as steam turbine-generators used to produce electric power, vibrations and other dynamic responses related to operation of the turbine-generator and its associated load may, if inadequately monitored and controlled, result in substantial risk of damage to the machine. For example, torsional vibrations of the main rotating shaft of the turbine-generator causes stresses which can damage or break the shaft. Also, imbalance in the external load applied to the machine can produce unbalanced currents in the output phase lines of the generator. These unbalanced currents, and particularly harmonics thereof, may interact to create torques near the resonant frequencies of certain components such as turbine buckets, which may lead to cracking or breaking of these buckets.
In order to fully assess the response of the turbine-generator to torsional vibrations and unbalanced currents, it is necessary to accurately monitor these parameters, preferably on a continuous basis. It is also desirable to obtain a permanent record of the data obtained during monitoring for subsequent analysis of machine behavior and implementation of corrective procedures. However, since turbine-generators are generally required to operate over extended periods of time, permanent records should be generated only at specified times such as during intervals when vibrations or harmonics of phase currents exceed predetermined levels.
Accordingly, it is an object of the present invention to provide improved apparatus for monitoring current and vibration signals of a turbine-generator.
It is also an object of the present invention to provide a system for monitoring phase currents and torsional vibrations of a three-phase turbine-generator which will generate an alarm signal and record current and torsional vibration signals if phase currents or torsional vibrations exceed preselected reference levels.
A further object of the present invention is to provide a monitoring system which in addition to fulfilling the above objects, will separate true components of shaft torsional vibration from false components present at frequencies that are multiples of the rate of rotation of the shaft.